This nonprovisional application claims priority under 35 U.S.C. xc2xa7119(a) on Patent Appliclation No. 2001-313644 filed in JAPAN on Oct. 11, 2001, which is herein incorporated by reference.
1. Field of the Invention
This invention relates to non-staining silicone rubber compositions for use as rubber construction materials such as sealants, coatings and gaskets.
2. Prior Art
Synthetic rubber sealants are commonly used to fill concrete joints, joints in window and door sashes, and around the edge of glass panels in buildings and other structures. A variety of such sealants are known, including silicone, polysulfide, polyurethane, acrylic rubber, styrene-butadiene rubber (SBR) and butyl rubber sealants. Of these, condensation-curing silicone sealants are widely used on account of their adhesive properties, heat and weather resistance, and durability. Solid gaskets used in construction are often made of peroxide-vulcanized silicone. In addition, techniques have recently been disclosed for overcoating peroxide-vulcanized silicone gaskets with a UV-curable silicone coating, and for fabricating gaskets integral to glass by placing a mold over the glass, pouring a platinum-catalyzed addition-curing silicone rubber composition into the mold, then curing the composition and bonding it to the glass.
However, one problem associated with the silicone sealants and gaskets used until now in exterior wall joints has been the spread of stains near the joints. This depends to a large extent on the site conditions (external environment, orientation) of the building and the joint design (shape, adhesion substrate), and has generally been found to correlate closely with the degree of air pollution around the building, the manner in which rainwater flows down over the building, and the degree of dryness after a rainfall. Solutions to prevent staining include changing the design of the joint to one which does not come into direct contact with rain, such as a hidden joint or a recessed joint, and using a coating to create a barrier on the surface of the sealant after it has cured or on the surface of the gasket. The former approach entails changes in the design specifications, leaving problems to be resolved with the decorative details of the building, whereas the latter approach requires the addition of a coating operation that increases overall construction costs. For these reasons, neither approach is in common use today.
We earlier disclosed that, when a rubber construction material such as a sealant, coating or gasket is made of the cured form of a silicone rubber composition containing dispersed particles having a photocatalytic activity, such as titanium oxide or zinc oxide, exposure to ultraviolet light modifies the surface, rendering it hydrophilic and non-staining (JP-A 9-227779). Yet, although this method marked a significant improvement in non-staining ability over other prior-art silicone sealants, there exists a need for better non-staining properties.
It is therefore an object of the present invention to provide silicone rubber compositions which have excellent non-staining properties.
We have found that silicone rubber compositions of the condensation curing type are significantly improved in non-staining properties by using as a base polymer a diorganopolysiloxane in which at least 2 mol % of the entire substituent radicals directly attached to silicon atoms are substituted or unsubstituted monovalent hydrocarbon radicals having at least two carbon atoms.
Accordingly, the invention provides a non-staining silicone rubber composition of the condensation curing type comprising a diorganopolysiloxane having at least two hydroxyl or hydrolyzable radicals each attached to a silicon atom per molecule as a base polymer, and a silane having at least two hydrolyzable radicals per molecule or a partial hydrolytic condensate thereof, wherein at least 2 mol % of the entire substituent radicals attached to silicon atoms in the diorganopolysiloxane are substituted or unsubstituted monovalent hydrocarbon radicals having at least two carbon atoms.